In spite of the major health issues surrounding heroin use, there have been few studies directly examining the impact of heroin on immune status. The present proposal seeks to further establish and extend the finding that the self-administration versus passive infusion of heroin induces a more pronounced inhibition of inducible nitric oxide synthase (iNOS), the enzyme responsible for the production of nitric oxide, a key molecule for host defense against bacterial infection. These studies are based on a literature detailing differential physiological effects of equivalent doses of drugs of abuse depending on whether drug infusions are self-controlled or passively infused. Specific Aim I tests the hypothesis that increasing the response requirement necessary to obtain heroin by self-administering animals will result in more pronounced differences in iNOS expression between self-administering and passively infused animals. One group of rats will be trained to press a lever for an infusion of heroin based on an increasing rate of reinforcement, such that increasing rates of responding on a lever will be necessary to receive an infusion of heroin. Two "partner" rats will receive equivalent, but passive infusions of either heroin or saline based on their first partner's lever pressing behavior. Specific Aim II tests the hypothesis that increasing drug intake by manipulating access time to self-administer heroin will result in greater reductions in iNOS expression in self administering animals than in animals receiving passive infusions of heroin. Evidence indicates that increased access time to self-administer drugs results in escalated drug-intake that is indicative of altered neurobiological mechanisms that may also affect immune responses such as iNOS expression. Specific Aim III tests the effects of self-administered and passively infused heroin on iNOS expression following challenge with representative strains of live Gram-negative Bacteroides and Gram-positive group B streptococci. For each series of experiments, the methods of real-time RT-PCR and western blotting will be used to quantify the effects of these manipulations on iNOS mRNA and protein levels. Together, these investigations will provide novel data concerning behavioral variables that alter heroin's effects on iNOS production, and provide a clinically relevant animal model to investigate the variables involved in the increased susceptibility of heroin users to infectious disease.